Rep. Paul D. Ryan led a parade of House Republicans Friday ripping into IRS Commissioner John Koskinen and the tax agency's handling of emails related to the targeting of conservative groups.

The Wisconsin Republican told the former Clinton and Bush administration official, who was brought in last year by the White House to clean up the IRS, "Nobody believes you."

Questions about the IRS and its handling of conservative groups during the early days of the Obama administration have ramped up dramatically in the past week, amid revelations the agency has irretrievably lost months of emails from Lois Lerner, the former IRS official at the center of the scandal.

Koskinen said Lerner's computer crashed in 2011 and her hard drive, along with the hard drives of other officials involved in the inquiries were recycled and likely destroyed.

"I want that hard drive and I want the hard drive of every computer that crashed," said Chairman Dave Camp, R-Mich.

Democrats on the panel apologized throughout the hearing to Koskinen for the interruptions and accusations levied by the Republicans.

The ranking Democrat on the committee, Rep. Sander M. Levin of Michigan, criticizing the tone of the questioning and said, "Witnesses deserve some respect."

Republicans countered by saying the apologies should be made to Americans targeted by the agency.

Camp, in an opening statement, said, "The American people have no reason to trust the IRS or, frankly, the Administration on this issue. To wait years to reveal the fact the IRS was targeting the American people, and then wait months to reveal that you are conveniently missing years of documents … well, it is no wonder I have heard the word “cover-up” thrown about a lot this week.